Biology subjects

Hannan, R. D.

Publications and source records attributed to Hannan, R. D..

12 recordsLinked to original sources

bioRxiv2025

Novel RNA Polymerase I and Cyclin Dependent Kinase combination therapy for the treatment of aggressive Acute Myeloid Leukemia.

Despite advances in therapy, specific subtypes Acute Myeloid Leukaemia (AML) remains largely incurable. The first-in-class RNA Polymerase I (Pol I) inhibitor, CX-5461, has demonstrated promising activity in both haematological malignancies and solid tumours by selectively inhibiting ribosome biogenesis to induce nucleolar stress, a critical vulnerability in rapidly proliferating cancer cells. CX-5461 has undergone clinical trials for the treatment of both solid and haematological malignancies, and 2nd generation Pol I inhibitor PMR-116 has also entered clinical trials, underscoring the translational potential of drugs that target RNA Polymerase I. To enhance the therapeutic efficacy of Pol I inhibition and prevent the emergence of resistance, we conducted a cell line-based unbiased screen of FDA-approved drugs to identify compounds that might synergise with CX-5461. This screen revealed that the pan-CDK inhibitors Dinaciclib and Flavopiridol enhance nucleolar stress pathway (NSP) activation and are strong candidates for combinatorial therapy with CX-5461. Further analysis showed that the combination of CX-5461 and Dinaciclib acts synergistically across a genetically diverse panel of human AML cell lines. This synergy is dependent on an intact NSP, with both agents independently stabilising p53, but with distinct phenotypic outcomes: Dinaciclib induces rapid apoptosis, whereas CX-5461 primarily enforces cell cycle arrest. This functional complementarity results in efficient tumour cell clearance and likely accounts for the delayed onset of therapy resistance. Importantly, combination treatment with CX-5461 and Dinaciclib significantly improved survival in murine models of AML and reduced colony formation in primary human AML samples. Together these findings provide preclinical evidence for a novel combination treatment strategy that leverages nucleolar stress and cell cycle control to enhance treatment outcomes in AML, paving the way for clinical translation of Pol I-CDK co-targeting therapies.

cancer biology↗

bioRxiv2025

Treatment with the ribosome biogenesis inhibitor CX-5461 increases platelet count in humans and enhances murine megakaryopoiesis

Thrombocytopenia is a common and serious complication of anticancer therapies. Here, we identify a novel thrombopoietic activity of the first-in-class ribosome biogenesis inhibitor CX-5461. In a phase I trial, 56% (9/16) of patients exhibited up to a 34% increase in platelet count following a single dose of CX-5461. In mice, CX-5461 elicited a rapid, reversible, and sustained [~]1.7-fold increase in platelet numbers without altering platelet function, lifespan, or inflammatory cytokines. Bone marrow analysis revealed a specific expansion of megakaryocytes (MKs), increased Sca1 MKs, and selective enrichment of MK-biased multipotent progenitor 2, independent of thrombopoietin (TPO) or c-mpl signalling. CX-5461 also mitigated carboplatin-induced thrombocytopenia, accelerating platelet recovery. Single-cell RNA sequencing and RNA velocity analysis confirmed enhanced differentiation of MK progenitors. These findings demonstrate that inhibition of ribosome biogenesis promotes TPO-independent megakaryopoiesis and identifies a previously unrecognised therapeutic opportunity to support platelet recovery in cancer treatment and potentially other thrombocytopenic states.

cell biology↗

bioRxiv2025

The novel RNA polymerase I transcription inhibitor PMR-116 exploits a critical therapeutic vulnerability in a broad-spectrum of high MYC malignancies.

Ribosome biogenesis (RiBi) is a key determinant of cell growth and proliferation and is highly elevated in cancer due to the activation by oncogenes such as MYC. First-generation RiBi inhibitor CX-5461, while demonstrating clinical potential for cancer treatment, also induces DNA damage through off-target inhibition of TOP2 and potentially other mechanisms, bringing into question RiBi as a target for cancer therapy. In this study, we test second-generation RiBi inhibitor, PMR-116. PMR-116 exhibits improved drug-like properties compared to first-generation RiBi inhibitors and has robust anti-tumour activity in the absence of global DNA damage signalling in a broad range of pre-clinical models of haematologic and solid cancers, particularly in malignancies where MYC is either the driver of disease or is elevated. Thus, our work demonstrates that RiBi is a genuine target for cancer therapy and highlights the potential to exploit a critical therapeutic vulnerability in high-MYC human cancers with dismal therapeutic outcomes. Statement of significanceDespite the development of new cancer therapies, most advanced malignancies remain incurable. We demonstrate that PMR-116, a second-generation RiBi inhibitor, has robust therapeutic efficacy in preclinical models of cancer, offering great promise to treat a broad spectrum of human solid and haematologic malignancies, especially where MYC is a driver.

cancer biology↗

bioRxiv2021

A new method for determining ribosomal DNA copy number shows differences between Saccharomyces cerevisiae populations

Ribosomal DNA genes (rDNA) encode the major ribosomal RNAs (rRNA) and in eukaryotic genomes are typically present as one or more arrays of tandem repeats. Species have characteristic rDNA copy numbers, ranging from tens to thousands of copies, with the number thought to be redundant for rRNA production. However, the tandem rDNA repeats are prone to recombination-mediated changes in copy number, resulting in substantial intra-species copy number variation. There is growing evidence that these copy number differences can have phenotypic consequences. However, we lack a comprehensive understanding of what determines rDNA copy number, how it evolves, and what the consequences are, in part because of difficulties in quantifying copy number. Here, we developed a genomic sequence read approach that estimates rDNA copy number from the modal coverage of the rDNA and whole genome to help overcome limitations in quantifying copy number with existing mean coverage-based approaches. We validated our method using strains of the yeast Saccharomyces cerevisiae with previously-determined rDNA copy numbers, and then applied our pipeline to investigate rDNA copy number in a global sample of 788 yeast isolates. We found that wild yeast have a mean copy number of 92, consistent with what is reported for other fungi but much lower than in laboratory strains. We also show that different populations have different rDNA copy numbers. These differences can partially be explained by phylogeny, but other factors such as environment are also likely to contribute to population differences in copy number. Our results demonstrate the utility of the modal coverage method, and highlight the high level of rDNA copy number variation within and between populations. Author summaryThe ribosomal RNA gene repeats (rDNA) form large tandem repeat arrays in most eukaryote genomes. Their tandem arrangement makes the rDNA prone to copy number variation, and there is increasing evidence that this copy number variation has phenotypic consequences. However, difficulties in measuring rDNA copy number hamper investigation into rDNA copy number dynamics and their significance. Here we developed a novel bioinformatics method for measuring rDNA copy number from whole genome sequence data that is based on the modal sequence read coverage. We established parameters for optimal performance of the method and validated it using yeast strains of known rDNA copy numbers. We then applied the method to a dataset of almost 800 global yeast isolates and demonstrate that yeast populations have different rDNA copy numbers that partially correlate with phylogeny. Our work provides a simple and accurate method for determining rDNA copy number that leverages the growing number of whole genome datasets, and highlights the dynamic nature of rDNA copy number.

genomics↗

bioRxiv2021

Nuclear stabilisation of p53 requires a functional nucleolar surveillance pathway

The nucleolar surveillance pathway (NSP) monitors nucleolar fidelity and responds to nucleolar stresses (i.e., inactivation of ribosome biogenesis) by mediating the inhibitory binding of ribosomal proteins (RPs) to mouse double minute 2 homolog (MDM2), a nuclear-localised E3 ubiquitin ligase, which results in p53 accumulation. Inappropriate activation of the NSP has been implicated in the pathogenesis of collection of human diseases termed "ribosomopathies", while drugs that selectively activate the NSP are now in trials for cancer. Despite the clinical significance, the precise molecular mechanism(s) regulating the NSP remain poorly understood. Using genome-wide loss of function screens, we demonstrate the ribosome biogenesis (RiBi) axis as the most potent class of genes whose disruption stabilises p53. Furthermore, we identified a novel suite of genes critical for the NSP, including a novel mammalian protein implicated in 5S ribonucleoprotein particle (5S-RNP) biogenesis, HEATR3. By selectively disabling the NSP, we unexpectedly demonstrate that a functional NSP is required for the ability of all nuclear acting stresses tested, including DNA damage, to robustly induce p53 accumulation. Together, our data demonstrates that the NSP has evolved as the dominant central integrator of stresses that regulate nuclear p53 abundance, thus ensuring RiBi is hardwired to cellular proliferative capacity.

cell biology↗

bioRxiv2020

Cohesin mutations are synthetic lethal with stimulation of WNT signaling

Mutations in genes encoding subunits of the cohesin complex are common in several cancers, but may also expose druggable vulnerabilities. We generated isogenic MCF10A cell lines with deletion mutations of genes encoding cohesin subunits SMC3, RAD21 and STAG2 and screened for synthetic lethality with 3,009 FDA-approved compounds. The screen identified several compounds that interfere with transcription, DNA damage repair and the cell cycle. Unexpectedly, one of the top hits was a GSK3 inhibitor, an agonist of Wnt signaling. We show that sensitivity to GSK3 inhibition is likely due to stabilization of {beta}-catenin in cohesin mutant cells, and that Wnt-responsive gene expression is highly sensitized in STAG2-mutant CMK leukemia cells. Moreover, Wnt activity is enhanced in zebrafish mutant for cohesin subunit rad21. Our results suggest that cohesin mutations could progress oncogenesis by enhancing Wnt signaling, and that targeting the Wnt pathway may represent a novel therapeutic strategy for cohesin mutant cancers.

cancer biology↗

bioRxiv2020

Psi promotes Drosophila wing growth through transcriptional repression of key developmental networks

Psi, the sole FUSE Binding Protein (FUBP) family single stranded DNA/RNA binding protein in Drosophila, is essential for proper cell and tissue growth, however its mechanism of function remains unclear. Here we use Targeted DamID combined with RNA-sequencing to generate the first genome-wide binding and expression profiles for Psi. Surprisingly, we demonstrate Psi drives growth in the Drosophila wing through transcriptional repression of key developmental pathways (e.g. Wnt, Notch and TGF{beta}). Thus, Psi patterns tissue growth by directly repressing transcription of developmental growth suppressors. Analysis of direct Psi targets identified novel growth inhibitors, including Tolkin (Zinc metallopeptidase implicated in TGF{beta} signalling), Ephexin (Rho-GEF) and emp (CD36 scavenger receptor-related protein). Their depletion not only suppressed impaired growth associated with Psi knockdown, but alone was sufficient to drive wing overgrowth. Thus, Psi drives wing growth twofold, through direct activation of Myc and through transcriptional repression of growth inhibitors comprising core developmental pathways.

developmental biology↗

bioRxiv2020

Transcriptional repression of Myc underlies AGO1's tumour suppressor function

Here we report novel tumour suppressor activity for the Drosophila Argonaute family RNA binding protein AGO1, a component of the miRNA-dependent RNA-induced silencing complex (RISC). The mechanism for growth inhibition does not, however, involve canonical roles as part of the RISC; rather AGO1 controls cell and tissue growth by functioning as a direct transcriptional repressor of the master regulator of growth, Myc. AGO1 depletion in wing imaginal discs drives a significant increase in ribosome biogenesis, nucleolar expansion, and cell growth in a manner dependent on Myc abundance. Moreover, increased Myc promoter activity and elevated Myc mRNA in AGO1 depleted animals requires RNA Pol II transcription. Further support for transcriptional AGO1 functions is provided by physical interaction with the RNA Pol II transcriptional machinery (chromatin remodelling factors and Mediator Complex), punctate nuclear localisation in euchromatic regions and overlap with Polycomb Group transcriptional silencing loci. Moreover, significant AGO1 enrichment is observed on the Myc promoter and AGO1 interacts with the Myc transcriptional activator Psi. Together our data show AGO1 functions outside of the RISC to repress Myc transcription and inhibit developmental cell and tissue growth.

developmental biology↗

bioRxiv2019

Reprogrammed mRNA translation drives metabolic response to therapeutic targeting of ribosome biogenesis

Elevated ribosome biogenesis in oncogene-driven cancers is commonly targeted by DNA-damaging cytotoxic drugs. Our first-in-human trial of CX-5461, a novel, less genotoxic agent that specifically inhibits ribosome biogenesis via suppression of RNA Polymerase I (Pol I) transcription, revealed single agent efficacy in refractory blood cancers. Despite this clinical response, patients were not cured. In parallel, we demonstrated a marked improvement in the in vivo efficacy of CX-5461 in combination with PI3K/AKT/mTORC1 pathway inhibitors. Here we show that this improved efficacy is associated with specific suppression of translation of mRNAs encoding regulators of cellular metabolism. Importantly, acquired resistance to this co-treatment is driven by translational re-wiring that results in dysregulated cellular metabolism and induction of a cAMP-dependent pathway critical for the survival of blood cancers including lymphoma and acute myeloid leukemia. Our studies identify the molecular mechanisms underpinning the response of blood cancers to selective ribosome biogenesis inhibitors and identify metabolic vulnerabilities that will facilitate the rational design of more effective regimens for Pol I-directed therapies.

cancer biology↗

bioRxiv2019

Targeting RNA Polymerase I transcription synergises with TOP1 inhibition in potentiating the DNA damage response in high-grade serous ovarian cancer

Limited effective therapeutic options are available for patients with recurrent high-grade serous carcinoma (HGSC), the most common histological subtype accounting for the majority of ovarian cancer deaths. We have shown efficacy in poly-ADP ribose polymerase (PARP) inhibitor-resistant HGSC for the RNA Polymerase I (Pol I) transcription inhibitor CX-5461 through its ability to activate a nucleolar-associated DNA damage response (DDR). Here, we screen the protein-coding genome to identify potential targets whose inhibition enhances the efficacy of CX-5461. We identify a network of cooperating inhibitory interactions, including components of homologous recombination (HR) DNA repair and DNA topoisomerase 1 (TOP1). We highlight that CX-5461 combined with topotecan, a TOP1 inhibitor used as salvage therapy in HGSC, induces robust cell cycle arrest and cell death in a panel of HR-proficient HGSC cell lines. The combination potentiates a nucleolar-associated DDR via recruitment of phosphorylated replication protein A (RPA) and ataxia telangiectasia and Rad3 related protein (ATR). CX-5461 plus low-dose topotecan cooperate to potently inhibit xenograft tumour growth, indicating the potential for this strategy to improve salvage therapeutic regimens to treat HGSC.

cancer biology↗

bioRxiv2019

PGRMC1 phosphorylation status and cell plasticity 1: glucose metabolism, mitochondria, and mouse xenograft tumorigenesis

Progesterone Receptor Membrane Component 1 (PGRMC1) is expressed in many cancer cells, where it is associated with detrimental patient outcomes. It contains phosphorylated tyrosines which evolutionarily preceded deuterostome gastrulation and tissue differentiation mechanisms. Here, we demonstrate that manipulating PGRMC1 phosphorylation status in MIA PaCa-2 (MP) cells imposes broad pleiotropic effects. Relative to parental cells over-expressing hemagglutinin-tagged wild-type (WT) PGRMC1-HA, cells expressing a PGRMC1-HA-S57A/S181A double mutant (DM) exhibited reduced levels of proteins involved in energy metabolism and mitochondrial function, and altered glucose metabolism suggesting modulation of the Warburg effect. This was associated with increased PI3K/Akt activity, altered cell shape, actin cytoskeleton, motility, and mitochondrial properties. An S57A/Y180F/S181A triple mutant (TM) indicated the involvement of Y180 in PI3K/Akt activation. Mutation of Y180F strongly attenuated mouse xenograft tumor growth. An accompanying paper demonstrates altered metabolism, mutation incidence, and epigenetic status in these cells, indicating that PGRMC1 phosphorylation strongly influences cancer biology.

cancer biology↗

bioRxiv2019

Inhibition of RNA Polymerase I Transcription Activates Targeted DNA Damage Response and Enhances the Efficacy of PARP Inhibitors in High-Grade Serous Ovarian Cancer

High-grade serous ovarian cancer (HGSOC) accounts for the majority of ovarian cancer and has a dismal prognosis. PARP inhibitors (PARPi) have revolutionized disease management of patients with homologous recombination (HR) DNA repair-deficient HGSOC. However, acquired resistance to PARPi by complex mechanisms including HR restoration and stabilisation of replication forks is a major challenge in the clinic. Here, we demonstrate CX-5461, an inhibitor of RNA polymerase I transcription of ribosomal RNA genes (rDNA), induces replication stress at rDNA leading to activation of DNA damage response and DNA damage involving MRE11-dependent degradation of replication forks. CX-5461 cooperates with PARPi in exacerbating DNA damage and enhances synthetic lethal interactions of PARPi with HR deficiency in HGSOC-patient-derived xenograft (PDX) in vivo. We demonstrate CX-5461 has a different sensitivity spectrum to PARPi and destabilises replication forks irrespective of HR pathway status, overcoming two well-known mechanisms of resistance to PARPi. Importantly, CX-5461 exhibits single agent efficacy in PARPi-resistant HGSOC-PDX. Further, we identify CX-5461-sensitivity gene expression signatures in primary and relapsed HGSOC. Therefore, CX-5461 is a promising therapy alone and in combination therapy with PARPi in HR-deficient HGSOC. CX-5461 is also an exciting treatment option for patients with relapsed HGSOC tumors that have poor clinical outcome.

cancer biology↗